While a brush motor mechanically switches electric contacts with a commutator etc., the brushless motor switches the energized directions from the controller side. Thus, for the energized directions to switch, it is necessary to detect a magnetic pole of a permanent magnet used for an internal rotor of the brushless motor, and a magnetic pole sensor such as a Hall effect device etc., has been used for simplification and cost cutting of a magnetic pole detection.
For this reason, it has been conventionally used to prolong the axial length of the permanent magnet used for an internal rotor up to a position where the magnetic pole sensor can detect the magnetic pole (Patent Document 1), and to utilize a separate magnet and magnetic materials in order to detect the magnetic pole of the permanent magnet used for the internal rotor (Patent Document 2).    Patent Document 1: JP-A2006-033989    Patent Document 2: JP-A2001-309618
The magnetic pole sensor is being used in the conventional brushless motor for detecting a rotational position of the internal rotor as discussed above. However, in the arrangement disclosed in Patent Document 1, as the axial length of the permanent magnet is prolonged, it becomes a factor of preventing weight and size reduction and cost cutting of the brushless motor. Further, as the arrangement disclosed in Patent Document 2 uses the separate magnet, it becomes a factor of obstructing the improvement of performance of the brushless motor due to the positional accuracy of the magnet with respect to the permanent magnet.
Moreover, it is desirable that the magnetic pole sensor is disposed at a position adjacent to the external stator as deployment of the magnetic pole sensor is important for a positional relationship to the external stator. In Patent Document 2, however, the magnetic pole sensor is not placed adjacent to the external stator, and the sensor is provided separately from that of the external stator. Therefore, the positioning of the magnetic pole sensor and the external stator is difficult as the positions of the external stator and the magnetic pole sensor are determined first at the final assembly. Furthermore, in general, the magnetic pole sensor is made of chips etc., and thus there is a problem that the magnetic pole sensor should have electrical insulation to the external stator.
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a brushless motor in which an insulation plate and a magnetic pole sensor are arranged to be able to dispose on one end of an external stator; the position of the magnetic pole of a permanent magnet formed integrally with a rotating shaft can be detected with precision without prolonging the permanent magnet; the positional relationship between the external stator and the magnetic pole sensor is excellently secured; and the insulating property of the magnetic pole sensor can be surely ensured.